1. Field of the Invention
The present invention relates to a motion assist device for assisting a periodical motion of a creature by applying a force to the creature.
2. Description of the Related Art
There has been disclosed in Japanese Patent Laid-open No. 2004-073649 (hereinafter, referred to as Patent Document 1) a device for assisting a periodical walking motion of a creature, such as a human, whose body such as a lower limb or the like is suffering from hypofunction, by applying a periodically varying force to the human. There has also been disclosed in Japanese Patent Laid-open No. 2007-061217 (hereinafter, referred to as Patent Document 2) a device for assisting or guiding a periodical motion of a human by adjusting strength of a force applied to the human according to a second model (spring model) representing a behavior property of a virtual elastic element so as to match a motion scale of the human to a desired motion scale thereof.
However, when using a plurality of models to determine a variation pattern of an assisting force, it may be difficult to match a motion rhythm of the creature to a desired motion rhythm thereof due to a time lag to a completion of a computation processing. Although computation processing load may be reduced so as to resolve the problem of the time lag by curtailing a part of models from the plurality of models, it may result in an inappropriate variation pattern of the assisting force from the viewpoint of matching the motion rhythm of the creature to the desired motion rhythm thereof. Moreover, according to the spring model, the strength of force applied to the human varies according to a pace of the periodical motion rhythm of the human. Therefore, when a human moves at a fast velocity of some extent, the periodical motion of the human can be assisted accordingly by a force sufficiently strong from the viewpoint of matching the motion scale to the desired motion scale of the human. However, on the other hand, when the human moves at a slow velocity due to severe physical hypofunction, the force applied to the human by the motion guiding device may be insufficient from the viewpoint of matching the motion scale to the desired motion scale of the human.